I turn 65 in a few months. When should I sign up for Medicare?

En español | If you already receive Social Security benefits, Social Security will automatically sign you up for Medicare Part A and Part B — though you can decline Part B enrollment if you want to. Otherwise, you need to apply for Medicare. The best time to do that depends entirely on your own situation. Broadly, there are two options:

During your Initial Enrollment Period (IEP):

This lasts for seven months, of which the fourth one is the month in which you turn 65. For example, if your 65th birthday is in June, your IEP begins March 1 and ends Sept. 30. (Exception: If your birthday falls on the first day of the month, the whole IEP moves forward one month. For example, if your birthday is June 1, your IEP begins Feb. 1 and ends Aug. 31.)

To avoid late penalties and delayed coverage, you need to sign up for Medicare during your IEP in these circumstances:

You have no other health insurance

You have health insurance that you bought yourself (not provided by an employer)

You have retiree benefits from a former employer (your own or your spouse’s)

You have COBRA coverage that extends the insurance you or your spouse received from an employer while working

You have veterans’ benefits from the VA health system (but no insurance provided by a current employer)

You’re in a nonmarital domestic relationship with someone of the same or opposite sex and you are covered by his or her employer insurance

If you enroll during the first three months of your IEP, your Medicare coverage begins on the first day of the month you turn 65 (or the first day of the previous month if your birthday falls on the first day of a month). If you sign up during the fourth month, coverage begins on the first day of the following month. But if you leave it until the fifth, sixth or seventh month, coverage will be delayed by two or three months. For example, if your birthday is in June and you sign up in September (the last month of your IEP), coverage will not begin until Dec. 1.

During your IEP you can also sign up for Medicare Part D prescription drug coverage — although you may not need to if you have “creditable” drug coverage from retiree benefits, COBRA or the VA. (“Creditable” means that Medicare considers the coverage as good as or better than Part D.) You also have the option to switch your coverage from Original Medicare to a Medicare Advantage plan (such as an HMO or PPO) during your IEP.

During a Special Enrollment Period (SEP)

This SEP is available only if you have health insurance (beyond the end of your IEP) from an employer for which you or your spouse actively works. It allows you to delay enrolling in Part B (and avoid its monthly premiums) until the employment or the coverage ends — whichever occurs first.

The SEP actually lasts throughout the time you have coverage from current employment and for up to eight months after it ends. If you enroll at any point during this time frame, your Medicare coverage will begin on the first day of the following month, and you will not be liable for late penalties — regardless of how old you are when you finally sign up.

Be aware that an IEP always trumps an SEP if the two should happen to overlap. For example, if your IEP ends on Aug. 31, and you retire on the same date, you will not be entitled to an SEP. Therefore, if you delayed enrollment until after Aug. 31, you would not be able to sign up until the following general enrollment period (Jan. 1 to March 31) and your coverage would not begin until July 1 — so you would be left for almost a year without coverage. Even if you signed up during the final months of your IEP, your coverage would still be delayed by two or three months. But, to continue this example, if you retired on Sept. 1, under the rules of the SEP, you could enroll in August and receive Medicare starting Sept. 1 with no loss of coverage.

If you will lose prescription drug coverage when the employer plan ends, you can sign up with a Medicare Part D drug plan. You will not be liable for late penalties if you enroll within two months of losing the employer coverage.

Two other Medicare enrollment scenarios have different rules:

If you live outside the United States:

If you live outside the United States, without either you or your spouse working, you have a difficult decision to make. You can either sign up for Part B and pay its monthly premiums, even though you can’t use Medicare services abroad — or you can wait to sign up until you return to the U.S. and then face getting hit with permanent late penalties and delayed coverage.

But if you or your spouse is working, and you have health insurance from an employer or are covered under the public national health system of the country where you live, you have the right to delay Medicare enrollment until the employment ends. You will then be entitled to the same SEP explained earlier in this section.

There is another exception: If you are not fully insured — that is, if you are not entitled to Part A benefits without paying premiums for them — you cannot sign up for either Part A or Part B while overseas. You can enroll within three months of returning to the United States to live permanently. In this situation, coverage begins on the first day of the month after you enroll, and you do not risk late penalties, regardless of how old you are or how long you’ve lived abroad.

Otherwise, if you want to sign up for Medicare while living outside the United States, you can apply through your nearest U.S. embassy or consulate. For contact information, go to https://www.usembassy.gov/ and select the country.

Part D drug coverage has different rules. On your return to live permanently in the United States, you’re entitled to a special enrollment period of up to three months (if you turned 65 abroad) or up to two months (if you turned 65 before leaving the U.S.) to sign up with a Part D drug plan without risking late penalties. Coverage begins on the first day of the month after you enroll.

If you are in prison:

If you turn 65 while living in prison or any other type of correctional institution, you can either enroll in Part B during your IEP and pay monthly premiums, even though you can’t use Medicare services while incarcerated — or wait until you’re released and then face permanent late penalties and delayed coverage.

Similarly, if you’re imprisoned after age 65 and already enrolled in Medicare, you’re expected to continue paying premiums to avoid penalties when you come out.

Part D drug coverage has different rules. On your release, you’re entitled to a special enrollment period of up to three months (if you turned 65 in prison) or up to two months (if you turned 65 before going to prison) to sign up with a Part D drug plan and avoid late penalties. Coverage begins on the first day of the month after you enroll.